Pollution has blackened and yellowed much of the facade, so a thorough cleaning has been prescribed to restore the building’s beauty.

Though tourist numbers have dropped at the Taj Mahal in recent years, tens of thousands of people still visit every day. (ATUL LOKE / THE NEW YORK TIMES)

NEW DELHI—For the first time ever, the Taj Mahal, India’s monument to eternal love, is getting a serious cleaning.

For more than 350 years, monsoon rains in Agra, the bustling city where the monument sits, were enough to wash dirt off the structure’s walls. But pollution has worsened over the last couple of decades, and parts of the marble facade have turned yellow and black.

Since 2015, workers have scaled the monument’s minarets and walls to correct discolouration and remove layers of grime from the 17th-century structure, which was built by Muslim emperor Shah Jahan as a mausoleum for his favourite wife, Mumtaz Mahal.

Behind the monument, the Yamuna River has also filled with sewage and other waste, worsening the problem by attracting millions of mosquito-like insects. They settle near the backside of the Taj Mahal and excrete a green substance on its walls during mating flights.

Cleaning the monument is time-consuming and challenging. To remove discolouration, workers suspended on scaffolding are caking Fuller’s earth — a mud paste that absorbs dirt, grease and animal excrement, and that is commonly used to treat skin impurities — on the entire monument. The mud is then washed off, leaving a pristine surface.

“No chemicals are used,” said Bhuvan Vikrama, a superintendent with the Archaeological Survey of India, which is overseeing the cleaning. “This is the best option, so far, that we have come across. We have been using it for decades on marble surfaces.”

Over the last few years, the scaffolding has mostly prevented people from taking unobstructed photographs of the monument. Workers have tried to clean the minarets in stages, in part to ensure that the millions of tourists who visit the Taj Mahal every year come away with a good view of the tomb, which Rabindranath Tagore, India’s celebrated poet, once compared to “a solitary tear suspended on the cheek of time.”

But this year, workers may face their biggest hurdle yet: restoring the monument’s dome to a pearly white. The metal scaffolds that workers used to apply mud paste to the minarets are too heavy and rigid to assemble around the dome, so a type of bamboo scaffolding, which was used for conservation work in the 1940s, is being considered instead.